Transcription of circular and linear DNAs in amphibian oocytes.
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Animals↗
Biomedical subjects
H Weintraub
Publications and source records attributed to H Weintraub.
Developmental aspects of chromatin structure and gene expression.
We have attempted to investigate the conformational basis and developmental relevance of globin-associated hypersensitive sites in avian and human cells. Our results indicate that once formed, DNaseI-hypersensitive sites have the capacity to propagate their own structure to daughter cells in the absence of the original events that have led to their formation. We postulate that the single-stranded character (as revealed by S1 nuclease) of these DNaseI-hypersensitivity sites could explain these results. In addition, we show that the locations of hypersensitive sites in an active avian endogenous retrovirus remain unmethylated in mature sperm and suggest that this phenomenon could lead to the propagation of structural information from germ line to fertilized egg. We have also investigated the chromatin structure of the chromosomal DNA regions containing the human G gamma-, A gamma-, delta-, and beta-globin structural genes in both fetal and adult erythropoietic tissues. Our results indicate that DNaseI introduces specific cuts into the beta-globin gene cluster in erythroid cells, but not in white blood cells. The predominant sites are located at the 5' sides of the G gamma-, A gamma-, delta-, and beta-globin genes, within 200 bp of the respective CAP sites. Examination of fetal liver cells has revealed the presence of hypersensitive sites at the 5' side of all four genes, whereas analysis of adult bone marrow has revealed the characteristic sites near the delta- and beta-globin genes but no hypersensitive sites at the 5' termini of the G gamma- or A gamma-globin genes. The presence of delta- and beta-hypersensitive sites in fetal cells suggests that the increment in expression of the delta and beta genes during development most likely involves the modulation of another pathway to gene expression.
Chromatin↗
[Demonstration of maturation promoting factor activity in Saccharomyces cerevisiae].
Microinjection of a crude yeast extract into fully grown immature Xenopus laevis oocytes induces the reinitiation of meiotic maturation as does Xenopus laevis oocyte MPF (Maturation Promoting Factor) by itself. Using several strains of yeast exhibiting temperature sensitive cell cycle block (cdc), it was observed that yeast extract exhibits MPF activity only when obtained during the time interval from the G2 period to the metaphase. This observation stresses eucaryotic ubiquity of MPF.
Animals↗
Propagation of globin DNAase I-hypersensitive sites in absence of factors required for induction: a possible mechanism for determination.
We tested whether DNAase I-hypersensitive sites, once induced, can be propagated to daughter cells in the absence of the original inducer. Chicken embryo fibroblasts infected with a temperature-sensitive Rous sarcoma virus at 41 degrees C and then shifted to 36 degrees C become transformed and begin to transcribe globin RNA. DNAase I-hypersensitive sites appear in the alpha- and beta-globin chromatin domains. Neither transcription nor hypersensitive sites are detected in cells infected and maintained at 41 degrees C. Activation of the globin hypersensitive sites occurs within 30 min of a temperature shift to 36 degrees C and does not require new protein synthesis. To test for the self-propagation of these hypersensitive structures, we inactivated the v-src gene product by a shift back up to 41 degrees C, and allowed the cells to divide 20 times at 41 degrees C. Although transcription of the globin genes was minimal after this treatment, the DNAase I-hypersensitive sites remained. The same sites can be induced by NaCl shock of cells. After the cells are returned to normal medium and allowed to grow for 20 doublings, the hypersensitive sites remain. This suggests that once formed, DNAase I-hypersensitive sites have the capacity to template their own structure independent of the initial "inductive" event. The single-stranded character of these DNAase I-hypersensitive sites could explain these results.
Animals↗
Temperature-sensitive changes in the structure of globin chromatin in lines of red cell precursors transformed by ts-AEV.
Chicken bone marrow cells infected in vitro with a temperature-sensitive avian erythroblastosis virus fall to produce hemoglobin at 36 degrees C. When the product or products of the transforming gene (erb) are inactivated by a temperature shift to 42 degrees C in culture, several different cloned lines of cells infected with the temperature-sensitive avian erythroblastosis virus begin to make hemoglobin. This shift in phenotype correlates with an increase in hemoglobin mRNA specific to both adult and embryonic alpha and beta globin. The switch is accompanied by the acquisition of DNAase I-hypersensitive sites in one cell line (clone 2); however, a hypothetically more mature line (clone 3) has already acquired globin DNAase-hypersensitive sites but does not express hemoglobin until the temperature shift. Several (but not all) specific restriction sites associated with both the alpha and beta domains become unmethylated after the switch from 36 degrees C to 42 degrees C. The magnitude of these methylation switches is small compared with changes that occur in these genes during normal avian erythropoiesis. The results suggest that changes in chromosomal structure precede transcription and are not a consequence of transcription. Since (presumptive) precursor cloned lines can be established with some, but not all, of the structural properties of active globin chromatin, it is likely that many of these properties can be independently established and are not obligatorily related.
Alpharetrovirus↗
An altered DNA conformation detected by S1 nuclease occurs at specific regions in active chick globin chromatin.
The single-stranded activity of S1-nuclease cleaves globin chromatin in red cell nuclei in specific regions. The cleavages are observed only in tissues in which the globin genes are active, and they "switch" to reflect the switching pattern of globin-gene expression in embryonic and adult red cells. The positions of the S1 cleavages in the beta- and alpha-globin chromatin correspond to the general region of known DNAase I-hypersensitive sites, but can be distinguished in detail. When DNA segments containing these regions are subcloned into pBR322 and the supercoiled molecules are treated with S1, similar sites are cleaved in the purified supercoiled (but not linear) recombinant plasmid DNA. However, the dominant S1 cutting sites are shifted in the plasmid vis-a-vis the chromatin. We believe that some aspect of DNA sequence is translated into an altered DNA structure in chromatin and that it is this altered structure that is recognized by s1 nuclease and possibly by certain chromosomal proteins. Several physical properties reflected in the S1 digestion of supercoiled plasmids suggest a mechanism for generating differences in daughter cells during development.
Animals↗
Tissue-specific and species-specific monoclonal antibodies to avian red cell nuclear proteins.
In order to identify potential red cell-specific regulatory proteins and to define additional red cell-specific markers, we have isolated a series of hybridomas that produce monoclonal antibodies that react with nuclear preparations from avian red blood cells. Several antibodies have been well characterized for their tissue- and species-specific reactions by using solid-phase and protein-transfer radioimmunoassays as well as immunofluorescence. These antibodies should allow isolation and characterization of individual nuclear proteins that are tissue and species specific and may prove useful for the study of gene expression in the erythropoietic system. The majority of the well-characterized antibodies appear to have tissue-specific properties. However, three antibodies react with all tested chicken tissues; one of these reacts with multiple peptides in a pattern that varies qualitatively and quantitatively between the tissues. This may reflect a common protein domain or modification that is used in several different tissues for similar functions but is nevertheless present in an overall protein framework that is tissue specific. Because the major fraction of the hybridomas initially produced is tissue specific, we presume that the immune system selects for tissue-specific determinants. This property of the immune system may prove to be a useful general feature of this type of analysis.
Animals↗
Chromatin structure of endogenous retroviral genes and activation by an inhibitor of DNA methylation.
The transcriptionally active ev-3 and inactive ev-1 endogenous retrovirus loci in chick cells differ in that ev-3 is undermethylated, preferentially sensitive to DNase I digestion, and contains nuclease hypersensitive sites in each of its two long terminal repeats. Transient exposure of cells to 5-azacytidine, a cytosine analogue which cannot be methylated at the 5 position, results in the hypomethylation and transcriptional activation of ev-1, as well as the acquisition of at least one nuclease-hypersensitive site within the chromosomal domain of ev-1.
Animals↗
Hormonal activation of protein kinase and lipid mobilization in the locust fat body in vitro.
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Animals↗
Isolation of actively transcribed nucleosomes using immobilized HMG 14 and 17 and an analysis of alpha-globin chromatin.
Taking advantage of the known specificity of interaction of HMG 14 and 17 with actively transcribed chromatin, we have covalently cross-linked these proteins to agarose and used this HMG 14-17 column to purify active nucleosomes. The column has been used to map the DNA regions surrounding the chicken alpha-globin genes for their capacity to bind HMG 14-17. The results show that at a crude level the HMG binding region correlates with the major stable primary transcript and the region of DNAase I sensitivity. At a finer level of analysis, however, the correspondence between DNAase I sensitivity and HMG binding is preserved, yet this chromosomal domain is shown to extend about 1 kb beyond the known primary transcript for the two chicken alpha genes. Why HMG 14 and 17 bind specifically to active nucleosomes is still not known. Our experiments suggest that at least one additional chemical difference distinguishes them. This difference is not reflected in the DNA:protein ratio; in the electrophoretic mobility of the particles or associated DNA; in the inner histone stoichiometry; in a marked degree of histone modification as assayed on Triton-urea gels; or in the presence of nonhistone proteins. Active nucleosomes can be dissociated and reconstituted and their ability to bind to HMG 14-17 restored. The ability to reconstitute binding should make it possible to determine whether the specificity for the interaction resides in the protein or the DNA.
Animals↗
Alpha-Globin-gene switching during the development of chicken embryos: expression and chromosome structure.
We have analyzed the chromosome structure and expression of the alpha-gene cluster in developing chicken embryos. Using recombinant lambda clones (Dodgson and Engel, 1980), we show a striking relationship between chromosomal regions that are unmethylated, regions that are DNAase I-sensitive and regions that are transcribed. Adjacent regions at both the 5' and 3' sides of the active alpha genes are methylated and relatively insensitive to DNAase I. The active alpha subdomain defined by these assays begins right at the 5' side of the first alpha gene (alpha D) in the active cluster in definitive red cells and extends through a 1.5 kb spacer, into the second alpha gene (alpha A), and 1.5 kb beyond the 3' side of that gene. The sharp boundaries of this subdomain suggest that specific DNA sequences may establish its borders. The extension of the active chromosomal domain beyond the most stable nuclear transcript suggests that transcription may proceed beyond the 3' ends of both alpha A and alpha D. This has been verified by in vitro runoff nuclear transcription. Presumably, poly(A) addition occurs before transcription is terminated. During the switch from the primitive to definitive lineage of erythroblasts, the so-called U gene becomes inactive. This inactivity is reflected in its assembly into a more DNAase-resistant structure. The associated DNA also becomes methylated, and no transcription is detectable by endogenous RNA polymerases. A DNAase I-hypersensitive region at the gene becomes inactivated after the switch to the definitive lineage.
Animals↗
Activation of globin genes during chicken development.
Hb first appears in the developing chicken blastoderm at 35 hr of incubation. We have isolated the presumptive Hb-forming area of the embryo at 20-23 hr and shown that most of the cells in this region are red cell precursors. The structure and activity of the globin genes in these precursors have been assayed in three ways: by runoff nuclear transcription to measure the number of initiated RNA polymerases present on the globin genes; by measuring the degree of methylation of these genes with methyl-sensitive restriction enzymes; and by monitoring the DNAase I sensitivity and the generation of DNAase I-hypersensitive sites in the globin chromatin. All these assays show the globin genes to be inactive in precursor cells. Additional experiments focusing on the mechanism of the transition from an inactive to an active chromosome structure indicate that DNA replication but not cytokinesis is intimately coupled to the transition process.
Animals↗
Tropomyosin is decreased in transformed cells.
The steady-state level and synthesis of a pair of polypeptides of Mr 33,000 and 35,000 in chicken embryo fibroblasts (CEF) transformed by Rous sarcoma virus (RSV) are significantly decreased relative to normal CEF; however, the decrease is more pronounced in the case of the Mr 35,000 polypeptide. These polypeptides have been identified as the alpha and beta subunits of CEF tropomyosin by selective staining with tropomyosin antibody, two-dimensional gel electrophoresis, partial peptide analysis, and solubility properties. The decrease in tropomyosin is shown to be a transformation-specific phenomenon in that it does not occur after infection with a virus deleted in src sequences. Decreased synthesis of tropomyosin is also observed in quail cells transformed by MC29 (a retrovirus with a different onc gene than that in RSV) and also in chemically transformed quail cells. The decreased in tropomyosin is probably not a direct result of the disruption of the microfilament system in transformed cells because disruption of the microfilament system with trypsin or cytochalasin B in normal CEF does not lead to a decrease in tropomyosin synthesis. A decrease in tropomyosin in CEF after transformation may be a result of a pleiotropic effect that results in the transcriptional inactivation not only of the tropomyosin gene but also of the fibronectin and procollagen genes described by others.
Animals↗
Transcriptional regulation of hemoglobin switching in chicken embryos.
We used recombinant chicken deoxyribonucleic acid clones containing embryonic and adult beta-globin genes and "runoff" endogenous nuclear transcription to investigate the expression of embryonic and adult beta-globin genes during hematopoiesis in the developing chicken embryo. Purified, cloned deoxyribonucleic acids were digested with various restriction enzymes, separated on agarose gels, blotted to nitrocellulose, and annealed with purified nuclear [32P]ribonucleic acid synthesized in vitro from embryonic or adult red cell nuclei. Transcription of the respective globin genes was assayed by hybridization of nuclear [32P]ribonucleic acid to specific restriction fragments containing adult or embryonic coding sequences. Our results indicate that little, if any, transcription from the adult or embryonic beta-globin genes is detectable in the heterologous red cell nuclei, even under conditions in which ribonucleic acid processing probably does not occur.
Animals↗
Recognition of specific DNA sequences in eukaryotic chromosomes.
The packaging of DNA into chromatin probably places certain restrictions on how specific DNA sequences can be recognized by DNA sequence specific recognition proteins (SRP). Several unique features of this type of interaction are discussed. Specifically, as a consequence of the coiling of the DNA about a histone core, it is proposed that DNA recognition sites will be compound and that each element of the compound recognition site will be about 10 - 20 b.p. in length and distributed at approximately 80 b.p. intervals--the periodicity of the DNA wrapping around the nucleosome.
Base Sequence↗
Antibodies to Pseudomonas testosteroni 3-oxosteroid delta 4-delta 5-isomerase.
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Animals↗
Electrophoretic separation of a class of nucleosomes enriched in HMG 14 and 17 and actively transcribed globin genes.
Monomer nucleosomes from chick erythrocytes can be fractionated according to their electrophoretic mobility in (comparatively) high salt acrylamide gels. We show that the fractionation is based predominantly on differences in charge. The monomer heterogeneity persists even when the nucleosomes are trimmed down to 145 bp with Exo III or when H1 and H5 are removed. The slowest migrating monomers are associated with HMG 14 and 17; however, we do not believe that these proteins are entirely responsible for the altered mobility since the nucleosome heterogeneity persists even after removal of HMG 14 and 17. The DNA associated with the HMG 14 and 17 containing nucleosomes is shown to be enriched in actively transcribed globin sequences.
Animals↗
Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo-steroid delta 4-delta 5-isomerase.
Studies of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Delta(4)-Delta(5)-isomerase with Delta(5(6))- and Delta(5(10))-steroid substrates demonstrate the importance of the position of the double bond for the efficiency of the isomerization process. Thus 3-oxo-Delta(5(6))-substrates have markedly high k(cat.) values, whereas those of 3-oxo-Delta(5(10))-substrates are very low and their apparent K(m) values approach equilibrium dissociation constants. The first step in the isomerization process is: [Formula: see text] which is governed by the k(-1)/k(+1) ratio and is shown to be very similar for the two classes of substrates (3-oxo-Delta(5(6))- and -Delta(5(10))-steroids). They therefore differ in the steps distal to the initial formation of the Michaelis-Menten complex. The use of the deuterated androst-5(6)-ene-3,17-dione substrate enabled us to calculate individual rate constants k(+1) and k(-1) as well as to determine the apparent rate-limiting step in the isomerization process. With the deuterated oestr-5(10)-ene-3,17-dione substrate, no significant isotope effect was observed suggesting that a different rate-limiting step may be operative in this isomerization process. Data are presented that indicate that under optimal concentrations of the efficient androst-5(6)-ene-3,17-dione substrate, the forward reaction for ES complex formation (as defined by k(+1)) is limited only by diffusion and the apparent K(m) does not approach the equilibrium constant, suggesting that the evolution of this enzyme has proceeded close to ;catalytic perfection'.
Androstenedione↗